A digital sign installed on the historic Lit Bros. building in January. A half-dozen more are planned between 7th and 13th Streets. (Steven M. Falk/Staff Photographer)

A Philadelphia taxi ride used to be one of those luxurious indulgences where you could escape, however briefly, from your over-scheduled life and spend a few precious minutes staring out the window, lost in thought. Now every trip begins with a backseat television screen laying claim to your eyeballs. At least you still have the option of hitting the off button.

If a bill sponsored by Councilman Mark Squilla is put to a final vote later this month, the mere act of walking through the streets of Center City will become a lot like a cab ride, but without the off button.

Squilla's bill has been crafted to give a Malvern-based billboard company exclusive rights for 25 years to place three enormous, high-definition, digital advertising displays in key downtown locations. Imagine structures the height of a rowhouse, wrapped in screens as sharp as the one inside the Comcast lobby, blasting advertising and public service videos 24 hours a day. Two would beam down on Broad Street, while the third would hover over us on 12th and Arch, across from the Reading Terminal Market.

Unlike digital billboards that mainly flash fixed images at us from the city's interstates, these displays would play full-motion, television-quality commercials. But because the screens would be housed in fanciful forms - one rendering shows an arm rising out of the sidewalk to support a massive globe - Squilla insists on describing them as a "marriage of art and architecture," rather than what they really are: billboards.

There seems to be no public space that Squilla, and his fellow Council members, believe can't be monetized. Over the last few years, they have proposed ads on schools, on street furniture, on vacant buildings. Squilla even tried to install a seven-story screen on a building at Seventh and Callowhill owned by Myron Berman, a major campaign donor ($7,400 since 2011). It was stopped at the eleventh hour when Mayor Nutter vetoed Squilla's bill.

But only since a digital sign was installed on the historic Lit Bros. store in January has the brave new world of outdoor video advertising become a reality in downtown. Blazingly bright, even during the day, the Market Street sign can be seen for blocks, and now dominates the view from Washington Square's pricey condos.

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That digital billboard was approved under a special Market Street sign district created by the city in 2011. Soon there will be a half-dozen more between Seventh and 13th Streets.

Like those condo owners, I initially found the Lits sign unsettling when I saw it glowing over Independence Mall, playing a slide show of ads for Dunkin' Donuts and Comcast. But I'm willing to accept it because it is intended to serve a public purpose.

The sign district was established as a way to finance the renovation of the scruffy retail corridor, and it includes guidelines for the types of signs that can be installed. To qualify, property owners must first put up $10 million for improvements. Because the promise of future ad revenue serves as equity, it enables building owners to obtain loans for renovation. The district is a large reason why the street has turned into a major construction zone.

The idea was the brainchild of Squilla's predecessor, Frank DiCiccio, and the Center City District's Paul Levy. When it was debated in Council in 2011, they predicted that the digital signs would transform Market Street into Philadelphia's own Times Square or Piccadilly Circus. The claim seemed dubious even then. Those spots are crossroads where people come together, while Market is a straight thoroughfare. The lineup of signs will never cohere into the same kind of energizing group composition.

The real selling point of the sign district was that it promised to contain those digital creatures in a limited geographic area. As screens become cheaper and more sophisticated, they're going to seep into more neighborhoods. The city already has made special exceptions for large digital displays outside the district at the Kimmel Center and in Dilworth Park and digital scrolls on newsstands and food trucks.

But just when we thought we had corralled the major screens into a single downtown zone, along comes Squilla with a bill for a second major sign district, one with a fancy name: Urban Experiential Displays, or UEDs. If his bill passes, what's to stop Council from declaring the entire city a giant sign district?

The Planning Commission was worried enough about the prospect to recommend that Council reject Squilla's bill. And Rina Cutler, deputy mayor for transportation, told me that, "as much as I like a little pizzazz, I have concerns about safety. There are enough distracted drivers as it is." It's unclear whether PennDot would even allow full-motion videos on heavily traveled streets such as Broad and Arch.

It's also troubling that Squilla's bill would directly benefit just one person: Thaddeus Bartkowski, owner of Catalyst Outdoor Advertising. Bartkowski has showered a total of $10,000 in campaign contributions on nine Council members, including $2,500 for Squilla ($2,600 is the limit for a single donor) and $2,000 for Kenyatta Johnson, whose district is slated for one of Catalyst's signs.

That's not all. The owners of Parkway Corp., Joseph and Robert Zuritsky, have donated $9,040 to Squilla since 2011. Two of their properties - Home2Suites and the Hyatt at the Bellevue garage - would host Bartkowski's signs. (The third sign, at Broad and Race, would be located on a small plaza owned by the Pennsylvania Convention Center.) It's worth noting that the Home2Suites' display would be 47 feet high and 26 feet wide - bigger than some Philadelphia trinities.

There are certainly other ways to sway support for Bartkowski's signs. As part of his proposal, Bartkowski is promising to give a small portion of his revenue as a "community benefit" to several civic organizations, including the Friends of the Rail Park, Avenue of the Arts, and Reading Terminal Market. Needless to say, the beneficiaries (with the exception of the Friends) have testified enthusiastically in favor of Squilla's bill.

Not only are Bartkowski's digital displays more intrusive than the Market Street signs, they're less lucrative for the city. Over the 25-year span of his contract, he would pay out a combined total of $5.2 million to the nonprofits to pay for maintenance projects - peanuts compared with what the Market Street sign district will generate.

In an age when government can barely fund the basics, dangling such funding before the city is awfully tempting. But in selling off the public realm for billboards, this bill will do more harm than good.